I generally start with the same base setup on all LMP and group c cars. Then I tweak and tweak, until it feels solid. The base tune I took from the 908 that I setup to what I consider damn near perfection.
I use the same base tune and weigh all of the cars out to about 935-945kg. Being that they all run the same ride heights and weights basically - that is why I have a little LMP base tune. People lower the diff specs way too much in a lot of the tunes they post online. They're doing it because they can't tighten up the front enough, because high locks will give you understeer.
The best tip I've been given is run spring rates on the soft side and struts/shocks on the stiff side. I note or less run the same shock and sway bar settings on most cars in the game. Ride height is key to pair the springs rates up with the strut properties.
The best tip I can give is to start learning how to set a car up with high rear lock settings and tightening up the front, until the car feels balanced out from front to back in terms of grip. I generally run initial torque (preload) and decel lock at the same right and about 10% less than the accel lock.
A high lock and preloaded diff carrier will really make or break the feeling of and your confidence in the car. It is so much more predictable. High initial torque will pin the rear to the ground quite better mid turn as will high decel lock and you'll be more stable under braking. High accel lock gets you romping turn exits like it's going out of style. You'll get more life out of the rear tires, too. Won't have to shirt shift at lower speeds as much, etc.
I build LS differentials for older bmws, so that kind of helps. Another thing - start the setup with high diff settings and tune it around that. Don't tune it, then monkey with the diff settings. You'll end up changing the tune around or setting the diff back to low lock rates to compensate.
Example - I run 55% lock on my E60 M5 in gt6. It weighs in at over 1300kg. I walk away from guys using tune out 458s, 12Cs, etc. And I notice some are even using aides aside from ABS. This is usually on the 24hr ring circuit. I often get the "damn, dude. That thing is quick!" "It is, isn't it."
A lot of people do not consider the fact that running low spring setting at a low ride high ≠ a soft springs no.matter the case. Consider the fact that the lower you go, with the same spring rates, the stiffer they become. It seems the spring modelling was done via progressive spring properties. So, you can set a car up fairly low with the right combos. Lower center of gravity is noticed as well on my end with a well setup car, compared to the same one with a higher ride height setup. They'll both be good tunes, but I'll notice the good setup with a lower COG helps a lot with lateral grip.
The problem is that it take hours to find sweet spots. There are cars that I've spent days to get where I wanted them to be. Believe it or not, my favorite car to drive is the bentley right now. I really like the 908. It feels like it has a vacuum sucking it to the ground, but the bentley can match it's times...somehow. I just think it is beautiful, so I was happy the car can be setup well.
When you drive the car, just adjust one thing at a time, too. Iron out the biggest short comings first.
